This invention concerns an improvement in the selective preparation of two-carbon atom oxygenated hydrocarbons, namely acetic acid, ethanol, and/or acetaldehyde, from synthesis gas. More particularly, the invention concerns reaction of synthesis gas in the presence of a catalyst containing rhodium in combination with molybdenum and/or tungsten under heterogeneous reaction conditions to produce a mixture of such two-carbon atom compounds in which ethanol is the major component.
The preparation of hydrocarbons and oxygenated hydrocarbons from synthesis gas (essentially a mixture of carbon monoxide and hydrogen with varying amounts of carbon dioxide) has received extensive study and has achieved commercial adoption. Reaction conditions generally involve temperatures on the order of 150.degree.-450.degree. C., pressures from atmospheric to about 10,000 psig, and hydrogen-to-carbon monoxide ratios in the range of 4:1 to about 1:4, with an iron group or a noble metal group hydrogenation catalyst.
One serious disability of most synthesis gas processes has been the non-selective or non-specific nature of the product distribution. Catalysts which possess acceptable activity generally tend to give a wide spectrum of products, for example, hydrocarbons and oxygenated hydrocarbons having a broad distribution of carbon atom contents. This not only complicates the recovery of desired products, but results in the wastage of reactants to commercially uninteresting byproducts.
Copending application Ser. Nos. 650,799, 541,660, and 590,717 describe processes for the selective preparation of two-carbon atom oxygenated hydrocarbons, namely, acetic acid, ethanol, and/or acetaldehyde, using rhodium-containing catalysts.